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Bring Back 1962-63

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About Bring Back 1962-63

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  1. Don, yes 2019 is currently at the lowest extent on record (for mid-October) at this early stage of the re-freeze season. I did an "Arctic Update" on the 2019-20 Winter Discussion/Forecast Thread yesterday and went into the reasons for this. I am not as pessimistic as some commentators and expect the re-freeze rate to increase substantially during this week and into next week, particularly on the Atlantic side of the Arctic which has seen very little growth at all so far. Here's the link to that post: https://www.33andrain.com/topic/1710-2019-20-winter-discussionforecast-thread/?do=findComment&comment=153515 I plan to produce a more comprehensive update on this "Arctic Thread" towards the end of this week. David
  2. ARCTIC WATCH I intend to do another comprehensive Arctic update later this week on the Arctic thread (link to the last one on Sept 27th: https://www.33andrain.com/topic/1367-the-arctic-thread/?do=findComment&comment=152787 ). In the meantime just a few indicators which are relevant to this thread - comments below each chart: The 2019 (red) re-freeze rate slowed down for much of last week following the second lowest ever minimum extent achieved on Sept 18th. The record low year of 2012 (black) saw a rapid recovery. 2019 is currently around the lowest extent on record "for this date". The year I have been focusing on is 2016 (orange) which saw the third lowest extent and an initial rapid recovery but then saw repeated stalls and even several setbacks from late Oct to the end of the year. I've read some very gloomy accounts about this year's recovery but I'm far less pessimistic than some commentators. 2016 had an awful lot against it - not least persistent WAA from the Atlantic and SSTs at their highest ever following the 2015/16 winter with the peak of the super Nino and the Atlantic jet powering into the Arctic for long periods pushing in much warmer currents and waters right up to the edge of the main ice sheet. The legacy of this is still evident today but the highest SST anomalies have gradually subsided to some extent. Although the last decade has seen a few years with stalling in the re-freeze, it does not follow that this year will continue that trend. The sea ice thickness charts are very revealing at this time of year. The summer ice retained close to the north of Svalbard is really encouraging but note that the ice edge has a really small area of blue shades (thickness below 0.75m) in that region before we see the green, yellow and orange shades with progressively thicker ice. This shows that there has been almost no new ice forming there and indeed the same applies in the north west Barents Sea and west Kara Sea (see my introductory post to the Arctic thread for an Arctic map with all the seas + many useful links: https://www.33andrain.com/topic/1367-the-arctic-thread/ ). New ice is advancing down the east coast of Greenland. By contrast, there has been considerable growth on the other side of the pole with a much wider band of new ice up to 0.25m (mauve). This distribution was largely due to WAA or "milder incursions" on the Atlantic side. These "were" greater than forecast: The last 7 days averaged about 1c more than expected across much of the Arctic - so nearer a +2.5c or higher anomaly. This changes around in the current 7 day anomaly forecast with the region around the pole and towards the Atlantic side much cooler, even below the 30 year mean over quite a wide area (which we do not see very often these days). Meanwhile the region on the far side of the pole will see temps rising. Now this "temp trend" is a key chart, particularly early on in the re-freeze season. This allows for the rapidly falling "mean" temps during October. If all else was equal (which it never is!) the whole chart would be blue! Again, most of the Atlantic side of the Arctic will see steady short term cooling. Interesting that much of central/northern Siberia will see a warmer period following the cold and early snow accumulation there (more below on that). Contrast that with the top chart. The deeper cold is shifting to north and west Russia and good to see northern Greenland getting very cold. The pressure charts for the next week to 10 days (not shown) show a mix of HP ridges and relatively weak LPs with no serious WAA and no major storms in the Arctic. Overall, although the re-freeze will slow down on the far side, much of the rest of the Arctic should see the rate increase substantially and that curve on the graph (top chart) "should" see a steady rise during the next few days. Let's hope that the recovery rate continues to rise during the second half of October. Last Sunday I posted the Siberian snow cover extent (see chart copied below) and the chart above shows that this has continued to increase - in fact it paused for a few days and then resumed its steady spread south westwards. Given the higher temps expected in Siberia this coming week, I would expect little further growth in Siberia but with much of northern and western Russia becoming very cold and an LP system pushing eastward through Russia around mid week we should see substantial snowfall there and the main snow area should expand steadily westwards. This will lead to the Eurasian snow cover being well ahead of normal for mid to later October. Overall it is a very mixed picture but with no cause for extreme pessimism at this stage. Displaced Arctic cold may provide lower temps in North America and Eurasia but it is bad news for the Arctic. The consequences for the impacts on ocean-atmosphere interaction and disconnects and changes to the jet stream are the subject of a great deal of research and no firm conclusions are yet available. I will place more of the recent papers on this into the Research Portal in the coming weeks and then I'll review the most relevant ones in several posts. David
  3. Well it depends which continent one is looking at! I appreciate that this is a "mostly" US forum. In western Europe and particularly in the UK 1962-63 saw our coldest winter since 1739-40 and the 2nd snowiest only just beaten by 1946-47! It was 1962-63 that led to my obsession with this wonderful subject from aged 9. The very low mean temps were mostly restricted to our part of the northern hemisphere with much of Eurasia seeing a normal winter and the eastern CONUS seeing a mild winter. http://www.markvoganweather.com/2015/12/05/a-look-back-winter-of-1962-63/ David EDIT: @Analog96 Yes, quite a contrast either side of the pond! I think much of eastern CONUS had a milder than average December and February but the far east had a colder than average January in 1962-63. The -NAO and a combination of Arctic, Greenland and (more occasional) Scandinavian HPs diverted many LPs just to the south of us and produced some memorable blizzards and certainly made us unusually snowy. EDIT 2: @Analog96 and @uncle w I stand corrected! I was looking at this link: http://www.deanfarr.com/state_weather/ I thought that I had set the area for New York but I had it set for all CONUS which overall had a milder than average Dec 1962 and February 1963 and a colder than average January 1963. You are of course, absolutely right about the eastern states having prolonged colder than average anomalies for the whole winter. The global anomalies for the 1962-63 winter are shown below: The chart uses the 1949-1978 30 year mean. If we applied the 1981 to 2010 mean, which is quite a lot higher, then the 1962-63 global -ve anomalies would look much greater. I couldn't find a separate USA anomaly chart using the contemporary means. The chart below is relative to the standard 1981-2010 mean:
  4. The Teleconnection of El Niño Southern Oscillation to the Stratosphere Authors: Daniela I.V. Domeisen, Chaim I. Garfinkel and Amy H. Butler Published: 30th November, 2018 Abstract: El Niño and La Niña events in the tropical Pacific have significant and disrupting impacts on the global atmospheric and oceanic circulation. El Niño Southern Oscillation (ENSO) impacts also extend above the troposphere, affecting the strength and variability of the stratospheric polar vortex in the high latitudes of both hemispheres, as well as the composition and circulation of the tropical stratosphere. El Niño events are associated with a warming and weakening of the polar vortex in the polar stratosphere of both hemispheres, while a cooling can be observed in the tropical lower stratosphere. These impacts are linked by a strengthened Brewer‐Dobson circulation. Anomalous upward wave propagation is observed in the extratropics of both hemispheres. For La Niña, these anomalies are often opposite. The stratosphere in turn affects surface weather and climate over large areas of the globe. Since these surface impacts are long‐lived, the changes in the stratosphere can lead to improved surface predictions on time scales of weeks to months. Over the past decade, our understanding of the mechanisms through which ENSO can drive impacts remote from the tropical Pacific has improved. This study reviews the possible mechanisms connecting ENSO to the stratosphere in the tropics and the extratropics of both hemispheres while also considering open questions, including nonlinearities in the teleconnections, the role of ENSO diversity, and the impacts of climate change and variability. Link to full paper: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1029/2018RG000596
  5. The importance of stratospheric initial conditions for winter North Atlantic Oscillation predictability and implications for the signal‐to‐noise paradox Authors: Christopher H. O'Reilly, Antje Weisheimer, Tim Woollings, Lesley J. Gray and Dave MacLeod Published: 12th October, 2018 Abstract: This study investigates the influence of atmospheric initial conditions on winter seasonal forecasts of the North Atlantic Oscillation (NAO). Hindcast (or reforecast) experiments – which differ only in their initial conditions – are performed over the period 1960–2009, using prescribed sea surface temperature (SST) and sea‐ice boundary conditions. The first experiment (“ERA‐40/Int IC”) is initialized using the ERA‐40 and ERA‐Interim reanalysis datasets, which assimilate upper‐air, satellite and surface observations; the second experiment (“ERA‐20C IC”) is initialized using the ERA‐20C reanalysis dataset, which assimilates only surface observations. The ensemble mean NAO skill is largest in ERA‐40/Int IC (r = 0.54), which is initialized with the superior reanalysis data. Moreover, ERA‐20C IC did not exhibit significantly more NAO hindcast skill (r = 0.38) than in a third experiment, which was initialized with incorrect (shuffled) initial conditions. The ERA‐40/Interim and ERA‐20C initial conditions differ substantially in the tropical stratosphere, where the quasi‐biennial oscillation (QBO) of zonal winds is not present in ERA‐20C. The QBO hindcasts are highly skilful in ERA‐40/Int IC – albeit with a somewhat weaker equatorial zonal wind amplitude in the lower stratosphere – but are incorrect in ERA‐20C IC, indicating that the QBO is responsible for the additional NAO hindcast skill; this is despite the model exhibiting a relatively weak teleconnection between the QBO and NAO. The influence of the QBO is further demonstrated by regressing out the QBO influence from each of the hindcast experiments, after which the difference in NAO hindcast skill between the experiments is negligible. Whilst ERA‐40/Int IC demonstrates a more skilful NAO hindcast, it appears to have a relatively weak predictable signal; this is the so‐called “signal‐to‐noise paradox” identified in previous studies. Diagnostically amplifying the (weak) QBO–NAO teleconnection increases the ensemble‐mean NAO signal with negligible impact on the NAO hindcast skill, after which the signal‐to‐noise problem seemingly disappears. Link to full paper: https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/qj.3413
  6. Sub-seasonal Predictability and the Stratosphere Authors: Amy Butler et al Published: 8th July, 2019 Abstract: The stratosphere and the troposphere are coupled in many ways. Because their interactions span days to weeks (or even longer), understanding these linkages and simulating them correctly in forecast models may provide a source of sub-seasonal to seasonal (S2S) prediction skill. This chapter reviews the tropical and extratropical coupling between the stratosphere and the troposphere and summarizes the most recent research showing how adequate simulation of the stratosphere may contribute to better prediction skill in the troposphere. Link to full paper: https://edwinpgerber.github.io/files/butler_etal-S2S-2019.pdf
  7. High‐latitude influence of the quasi‐biennial oscillation Authors: James A. Anstey and Theodore G. Shepherd Published: 28th March, 2013 Abstract: The interannual variability of the stratospheric winter polar vortex is correlated with the phase of the quasi‐biennial oscillation (QBO) of tropical stratospheric winds. This dynamical coupling between high and low latitudes, often referred to as the Holton–Tan effect, has been the subject of numerous observational and modelling studies, yet important questions regarding its mechanism remain unanswered. In particular it remains unclear which vertical levels of the QBO exert the strongest influence on the winter polar vortex, and how QBO–vortex coupling interacts with the effects of other sources of atmospheric interannual variability such as the 11‐year solar cycle or the El Niño Southern Oscillation. As stratosphere‐resolving general circulation models begin to resolve the QBO and represent its teleconnections with other parts of the climate system, it seems timely to summarize what is currently known about the QBO's high‐latitude influence. In this review article, we offer a synthesis of the modelling and observational analyses of QBO–vortex coupling that have appeared in the literature, and update the observational record. Link to full paper: https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/qj.2132
  8. Optimization of Gravity Wave Source Parameters for Improved Seasonal Prediction of the Quasi-Biennial Oscillation Authors: Cory A. Barton, John P. McCormack and Karl W. Hoppel Published: 9th September, 2019 Abstract: A methodology is presented for objectively optimizing nonorographic gravity wave source parameters to minimize forecast error for target regions and forecast lead times. In this study, we employ a high-altitude version of the Navy Global Environmental Model (NAVGEM-HA) to ascertain the forcing needed to minimize hindcast errors in the equatorial lower stratospheric zonal-mean zonal winds in order to improve forecasts of the quasi-biennial oscillation (QBO) over seasonal time scales. Because subgrid-scale wave effects play a large role in driving the QBO, this method leverages the nonorographic gravity wave drag (GWD) parameterization scheme to provide the necessary forcing. To better constrain the GWD source parameters, we utilize ensembles of NAVGEM-HA hindcasts over the 2014–16 period with perturbed source parameters and develop a cost function to minimize errors in the equatorial lower stratosphere compared to analysis. Thus, we may determine the set of GWD source parameters that yields a forecast state that most closely agrees with observed QBO winds over each optimization time interval. Results show that the source momentum flux and phase speed spectrum width are the most important parameters. The seasonal evolution of optimal parameter value, specifically a robust semiannual periodicity in the source strength, is also revealed. Changes in optimal source parameters with increasing forecast lead time are seen, as the GWD parameterization takes on a more active role as QBO driver at longer forecast lengths. Implementation of a semiannually varying source function at the equator provides RMS error improvement in QBO winds over the default constant value. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JAS-D-19-0077.1
  9. Simulating the QBO in an Atmospheric General Circulation Model: Sensitivity to Resolved and Parameterized Forcing Authors: James A. Anstey, John F. Scinocca and Martin Keller Published: 3rd March, 2016 Abstract: The quasi-biennial oscillation (QBO) of tropical stratospheric zonal winds is simulated in an atmospheric general circulation model and its sensitivity to model parameters is explored. Vertical resolution in the lower tropical stratosphere finer than ≈1 km and sufficiently strong forcing by parameterized nonorographic gravity wave drag are both required for the model to exhibit a QBO-like oscillation. Coarser vertical resolution yields oscillations that are seasonally synchronized and driven mainly by gravity wave drag. As vertical resolution increases, wave forcing in the tropical lower stratosphere increases and seasonal synchronization is disrupted, allowing quasi-biennial periodicity to emerge. Seasonal synchronization could result from the form of wave dissipation assumed in the gravity wave parameterization, which allows downward influence by semiannual oscillation (SAO) winds, whereas dissipation of resolved waves is consistent with radiative damping and no downward influence. Parameterized wave drag is nevertheless required to generate a realistic QBO, effectively acting to amplify the relatively weaker mean-flow forcing by resolved waves. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JAS-D-15-0099.1
  10. Constraints on Wave Drag Parameterization Schemes for Simulating the Quasi-Biennial Oscillation. Part II: Combined Effects of Gravity Waves and Equatorial Planetary Waves Authors: Lucy J. Campbell and Theodore G. Shepherd Published: 1st December, 2005 Abstract: This study examines the effect of combining equatorial planetary wave drag and gravity wave drag in a one-dimensional zonal mean model of the quasi-biennial oscillation (QBO). Several different combinations of planetary wave and gravity wave drag schemes are considered in the investigations, with the aim being to assess which aspects of the different schemes affect the nature of the modeled QBO. Results show that it is possible to generate a realistic-looking QBO with various combinations of drag from the two types of waves, but there are some constraints on the wave input spectra and amplitudes. For example, if the phase speeds of the gravity waves in the input spectrum are large relative to those of the equatorial planetary waves, critical level absorption of the equatorial planetary waves may occur. The resulting mean-wind oscillation, in that case, is driven almost exclusively by the gravity wave drag, with only a small contribution from the planetary waves at low levels. With an appropriate choice of wave input parameters, it is possible to obtain a QBO with a realistic period and to which both types of waves contribute. This is the regime in which the terrestrial QBO appears to reside. There may also be constraints on the initial strength of the wind shear, and these are similar to the constraints that apply when gravity wave drag is used without any planetary wave drag. In recent years, it has been observed that, in order to simulate the QBO accurately, general circulation models require parameterized gravity wave drag, in addition to the drag from resolved planetary-scale waves, and that even if the planetary wave amplitudes are incorrect, the gravity wave drag can be adjusted to compensate. This study provides a basis for knowing that such a compensation is possible. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JAS3617.1
  11. Constraints on Wave Drag Parameterization Schemes for Simulating the Quasi-Biennial Oscillation. Part I: Gravity Wave Forcing Authors: Lucy J. Campbell and Theodore G. Shepherd Published: 1st December, 2005 Abstract: Parameterization schemes for the drag due to atmospheric gravity waves are discussed and compared in the context of a simple one-dimensional model of the quasi-biennial oscillation (QBO). A number of fundamental issues are examined in detail, with the goal of providing a better understanding of the mechanism by which gravity wave drag can produce an equatorial zonal wind oscillation. The gravity wave–driven QBOs are compared with those obtained from a parameterization of equatorial planetary waves. In all gravity wave cases, it is seen that the inclusion of vertical diffusion is crucial for the descent of the shear zones and the development of the QBO. An important difference between the schemes for the two types of waves is that in the case of equatorial planetary waves, vertical diffusion is needed only at the lowest levels, while for the gravity wave drag schemes it must be included at all levels. The question of whether there is downward propagation of influence in the simulated QBOs is addressed. In the gravity wave drag schemes, the evolution of the wind at a given level depends on the wind above, as well as on the wind below. This is in contrast to the parameterization for the equatorial planetary waves in which there is downward propagation of phase only. The stability of a zero-wind initial state is examined, and it is determined that a small perturbation to such a state will amplify with time to the extent that a zonal wind oscillation is permitted. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JAS3616.1 I would like to thank Tom @Isotherm for recommending this paper.
  12. Momentum Flux and Flux Divergence of Gravity Waves in Directional Shear Flows over Three-Dimensional Mountains Authors: Xin Xu, Yuan Wang and Ming Xue Published: 6th June, 2012 Abstract: Linear mountain wave theory is used to derive the general formulas of the gravity wave momentum flux (WMF) and its vertical divergence that develop in directionally sheared flows with constant vertical shear. Height variations of the WMF and its vertical divergence are studied for a circular bell-shaped mountain. The results show that the magnitude of the WMF decreases with height owing to variable critical-level height for different wave components. This leads to continuous—rather than abrupt—absorption of surface-forced gravity waves, and the rate of absorption is largely determined by the maximum turning angle of the wind with height. For flows turning substantially with height, the wave momentum is primarily trapped in the lower atmosphere. Otherwise, it can be transported to the upper levels. The vertical divergence of WMF is oriented perpendicularly to the right (left) of the mean flow that veers (backs) with height except at the surface, where it vanishes. First, the magnitude of the WMF divergence increases with height until reaching its peak value. Then, it decreases toward zero above that height. The altitude of peak WMF divergence is proportional to the surface wind speed and inversely proportional to the vertical wind shear magnitude, increasing as the maximum wind turning angle increases. The magnitude of the peak WMF divergence also increases with the maximum wind turning angle, but it in general decreases as the ambient flow Richardson number increases. Implications of the findings for treating mountain gravity waves in numerical models are discussed. Link to full paper: http://twister.ou.edu/papers/Xu_Wang_XueJAS2012.pdf I would like to thank Tom @Isotherm for recommending this paper.
  13. A Review of Ocean/Sea Subsurface Water Temperature Studies from Remote Sensing and Non-Remote Sensing Methods Authors: Elahe Akbari, Seyed Kazem Alavipanah, Mehrdad Jeihouni, Mohammad Hajeb, Dagmar Haase and Sadroddin Alavipanah Published: 14th December, 2017 Abstract: Oceans/Seas are important components of Earth that are affected by global warming and climate change. Recent studies have indicated that the deeper oceans are responsible for climate variability by changing the Earth’s ecosystem; therefore, assessing them has become more important. Remote sensing can provide sea surface data at high spatial/temporal resolution and with large spatial coverage, which allows for remarkable discoveries in the ocean sciences. The deep layers of the ocean/sea, however, cannot be directly detected by satellite remote sensors. Therefore, researchers have examined the relationships between salinity, height, and temperature of the oceans/Seas to estimate their subsurface water temperature using dynamical models and model-based data assimilation (numerical based and statistical) approaches, which simulate these parameters by employing remotely sensed data and in situ measurements. Due to the requirements of comprehensive perception and the importance of global warming in decision making and scientific studies, this review provides comprehensive information on the methods that are used to estimate ocean/sea subsurface water temperature from remotely and non-remotely sensed data. To clarify the subsurface processes, the challenges, limitations, and perspectives of the existing methods are also investigated. Link to full paper: https://www.mdpi.com/2073-4441/9/12/936/htm
  14. A decadal tropical Pacific condition unfavorable to central Pacific El Niño Authors: Wenxiu Zhong, Xiao‐Tong Zheng and Wenju Cai Published: 28th July, 2017 and text corrected and updated on 9th April, 2018 Abstract: The frequency of central Pacific (CP) El Niño events displays strong decadal variability but the associated dynamics are unclear. The Interdecadal Pacific Oscillation (IPO) and the tropical Pacific decadal variability (TPDV) are two dominant modes of tropical Pacific decadal variability that can interact with high‐frequency activities. Using a 500 year control integration from the Geophysical Fluid Dynamics Laboratory Earth System Model, we find that the difference in mean state between the low‐frequency and high‐frequency CP El Niño periods is similar to the decadal background condition concurrently contributed by a negative IPO and a positive TPDV. This decadal state features strengthened trade winds west of the International Date Line and anomalous cool sea surface temperatures across the central tropical Pacific. As such, positive zonal advection feedback is difficult to be generated over the central to western tropical Pacific during the CP El Niño developing season, resulting in the low CP El Niño frequency. Link to full paper: https://agupubs.onlinelibrary.wiley.com/doi/epdf/10.1002/2017GL073846
  15. Impacts of Broad-Scale Surface Freshening of the Southern Ocean in a Coupled Climate Model Authors: Ariaan Purich, Matthew H. England, Wenju Caia, Arnold Sullivan and Paul J. Durack Published: 5th March, 2018 Abstract: The Southern Ocean surface has freshened in recent decades, increasing water column stability and reducing upwelling of warmer subsurface waters. The majority of CMIP5 models underestimate or fail to capture this historical surface freshening, yet little is known about the impact of this model bias on regional ocean circulation and hydrography. Here experiments are performed using a global coupled climate model with additional freshwater applied to the Southern Ocean to assess the influence of recent surface freshening. The simulations explore the impact of persistent and long-term broad-scale freshening as a result of processes including precipitation minus evaporation changes. Thus, unlike previous studies, the freshening is applied as far north as 55°S, beyond the Antarctic ice margin. It is found that imposing a large-scale surface freshening causes a surface cooling and sea ice increase under preindustrial conditions, because of a reduction in ocean convection and weakened entrainment of warm subsurface waters into the surface ocean. This is consistent with intermodel relationships between CMIP5 models and the simulations, suggesting that models with larger surface freshening also exhibit stronger surface cooling and increased sea ice. Additional experiments are conducted with surface salinity restoration applied to capture observed regional salinity trends. Remarkably, without any mechanical wind trend forcing, these simulations accurately represent the spatial pattern of observed surface temperature and sea ice trends around Antarctica. This study highlights the importance of accurately simulating changes in Southern Ocean salinity to capture changes in ocean circulation, sea surface temperature, and sea ice. Link to full paper: https://journals.ametsoc.org/doi/pdf/10.1175/JCLI-D-17-0092.1
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